Function prepare_update_entity_plan 

pub async fn prepare_update_entity_plan(
    runtime: &KhiveRuntime,
    token: &NamespaceToken,
    id: Uuid,
    patch: EntityPatch,
) -> RuntimeResult<AtomicOpPlan>

Build an entity update plan from a typed patch. Proposal changesets use this entry point so their explicit description: null clear operation is preserved instead of being collapsed by raw verb deserialization.